ASoC: audio-graph-card2-custom-sample.dtsi: add DPCM sample (Multi)

This patch adds DPCM link Multi-CPU/Codec sample to
audio-graph-card2-custom-sample.dtsi.
This sample is assuming MIXer connection.
One note is that Multi-FE is not supported on ASoC

	FE		BE
		****	+-+
	CPU5 -- *  * -- | | -- Codec4
	CPU6 -- *  *	| | -- Codec5
		****	+-+

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87pmsalu2s.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>